Active patient risk prediction

ABSTRACT

Electronic health records of a plurality of patients are received. A risk prediction model for a disease based on the electronic health records of the plurality of patients is created. An electronic health record of an original patient is received. A neighboring group of patients of the plurality of patients is identified, wherein the neighboring group of patients is two or more patients similar to the original patient. An ordering of the two or more patients of the neighboring group of patients is received, wherein the ordering of the two or more patients of the neighboring group of patients is based upon how similar each patient of the two or more patients is to the original patient. The risk prediction model is updated based on the ordering of the two or more patients of the neighboring group of patients.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of active learning,and more particularly to predicting the risk of patients to certaindiseases using electronic health records (EHR) along with activelearning with relative similarities.

Active learning has been extensively studied and successfully applied tosolve real world problems. The typical setting of active learningmethods is to query absolute questions. The key idea of active learningis that a machine learning algorithm can achieve higher accuracy withfewer training labels if it is allowed to choose the data from which itlearns. Active learning extends machine learning by allowing learningalgorithms to typically query the labels from an oracle (e.g., a humanannotator) that already understands the problem for currently unlabeledinstances. Though enormous progress has been made in the active learningfield in recent years, traditional active learning assumes that thequestions prompted by a machine can be confidently answered by humanexperts, which may not be the case in many real world applications.

In a medical application where the goal is to predict the risk ofpatients on certain diseases using EHR, the absolute questions may takethe form of, “Will this patient suffer from Alzheimer's later in his/herlife?” or, “Are these two patients similar or not?” Due to the excessiverequirements of domain knowledge, such absolute questions are usuallydifficult to answer, even for experienced medical experts. In addition,the performance of absolute question focused active learning methods isless stable, since incorrect answers often occur which can bedetrimental to the risk of the prediction model.

SUMMARY

Embodiments of the present invention include a method, computer programproduct, and system for updating a patient risk prediction model. In oneembodiment, electronic health records of a plurality of patients arereceived. A risk prediction model for a disease based on the electronichealth records of the plurality of patients is created. An electronichealth record of an original patient is received. A neighboring group ofpatients of the plurality of patients is identified, wherein theneighboring group of patients is two or more patients similar to theoriginal patient. An ordering of the two or more patients of theneighboring group of patients is received, wherein the ordering of thetwo or more patients of the neighboring group of patients is based uponhow similar each patient of the two or more patients is to the originalpatient. The risk prediction model is updated based on the ordering ofthe two or more patients of the neighboring group of patients.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a data processing environment,in accordance with an embodiment of the present invention;

FIG. 2 is a flowchart depicting operational steps of a program foractive patient risk prediction, in accordance with an embodiment of thepresent invention; and

FIG. 3 depicts a block diagram of components of a computing systemrepresentative of the computer of FIG. 1, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention allow for the updating of a patientrisk prediction model. The active patient risk prediction (ARP) programreceives electronic health records for an original patient, the subjectof the risk prediction, and a group of patients from which to create therisk prediction model. The ARP program creates the risk prediction modelfrom the group of patients and then identifies a smaller (neighboring)group of patients from the group of patients that is similar to theoriginal patient. An expert orders the group of patients and theoriginal patient based upon their similarities. The ARP program receivesthis ordering and updates the risk prediction model. Determiningneighboring groups of patients, ordering them, and then updating therisk prediction model based upon the ordering can happen any number oftimes and the goal is to create an accurate risk prediction model. ARPprogram then predicts the risk of the original patient suffering adisease, or diseases, based upon the risk prediction model.

Some embodiments of the present invention recognize that active patientrisk prediction (ARP), is a way to explore easier active learning formedical data, so as to address the dilemma when medical experts cannotconfidently provide absolute labels for patients. Asking easierquestions can effectively reduce the time and cost when applying activelearning techniques to real world problems. A key step to active patientrisk prediction is to select informative queries, by answering whichprediction model is improved maximally. The present invention, ratherthan asking for absolute questions such as labels, asks humans to placean ordering (possibly partial ordering) on the relative similarity ofthe neighbors to the instance that they are neighbors of.

Specifically, a computer prompts a patient along with the patients whoare similar to him/her (nearest neighbors), and then a medical expert isasked to sort or partially sort (from the most similar one to the leasesimilar one) the neighboring patients according to the relativesimilarity to the patient that they are neighbors of. Since the activelearning scheme is performed on neighbor sets rather than instances, thefocus is on selecting the most informative neighbor sets which is casedas a counting set cover problem. Counting set cover is an efficientcombinational algorithm to perform entity ranking/selection, and byusing, the aim is to locate the instance whose neighborhood is mostinfluential to the graph structure. This query scheme selects the mostinformative neighborhood to query, and the advice of the human expertsare enforced as constraints in the subsequent updating of theneighborhood structure, which is later used to help better propagatelabels on the graph with the process being repeated.

The main advantage of querying neighborhood structure/weights is thatthe relative questions are easier to answer for medical experts. This isparticularly useful to active learning in many specialized domains, suchas the medical field, where the absolute questions are difficult toanswer even for people with proficient domain knowledge. Additionally,the benefits of using a counting set cover algorithm to estimate theimportance of a patient neighborhood include: (i) neighbor sets that areessential to maintain the graph structure can be naturally found throughsolving a set cover problem; and (ii) counting with different weightingschemes would emphasize different notions of the importance of graphstructure, which enriches the flexibility of active neighborhoodselection.

The present invention will now be described in detail with reference tothe Figures. FIG. 1 is a functional block diagram illustrating a dataprocessing environment, generally designated 100, in accordance with oneembodiment of the present invention. FIG. 1 provides only anillustration of one implementation and does not imply any limitationswith regard to the systems and environments in which differentembodiments may be implemented. Many modifications to the depictedembodiment may be made by those skilled in the art without departingfrom the scope of the invention as recited by the claims.

An embodiment of data processing environment 100 includes computer 110,interconnected over network 102. Network 102 can be, for example, alocal area network (LAN), a telecommunications network, a wide areanetwork (WAN) such as the Internet, or any combination of the three, andinclude wired, wireless, or fiber optic connections. In general, network102 can be any combination of connections and protocols that willsupport communications between computer 110 and any other computerconnected to network 102, in accordance with embodiments of the presentinvention.

In example embodiments, computer 110 may be a laptop, tablet, or netbookpersonal computer (PC), a desktop computer, a personal digital assistant(PDA), a smart phone, or any programmable electronic device capable ofcommunicating with any computing device within data processingenvironment 100. In certain embodiments, computer 110 collectivelyrepresents a computer system utilizing clustered computers andcomponents (e.g., database server computers, application servercomputers, etc.) that act as a single pool of seamless resources whenaccessed by elements of data processing environment 100, such as in acloud computing environment. In general, computer 110 is representativeof any electronic device or combination of electronic devices capable ofexecuting computer readable program instructions. Computer 110 mayinclude components as depicted and described in further detail withrespect to FIG. 3, in accordance with embodiments of the presentinvention.

Computer 110 includes active patient risk program (ARP) program 112 andelectronic health record (EHR) database 114. ARP program 112 is aprogram, application, or subprogram of a larger program that creates arisk prediction model for a disease using EHRs. ARP program 112 thendetermines a neighboring group of patients to the original patient usingthe risk prediction model and medical experts rank the neighboring groupof patients and the original patient. ARP program 112 then updates therisk prediction model using the rankings, and estimates risk that apatient will suffer from a certain disease. EHR database 114 containsmedical information about individual patients. An EHR is a record indigital format that is theoretically capable of being shared acrossdifferent health care settings and may include a wide range of data,including, but not limited to, demographics, medical history, medicationand allergies, immunization status, laboratory test results, radiologyimages, vital signs, and personal statistics like age and weight.

ARP program 112 receives EHRs about multiple patients including thesubject patient that will have their risk estimated for a certaindisease. ARP program 112 creates a risk prediction model from the EHRsof the multiple patients. ARP program 112 identifies a neighboring groupof patients, from the multiple patients, that the subject patient isclose in risk for the disease based on the risk prediction model andnotifies medical experts of the determined neighboring group ofpatients. ARP program 112 receives an ordering of the neighboring groupof patients and the subject patient from the medical experts based onthe risk of the disease. ARP program 112 updates the risk predictionmodel based on the ordering of the neighboring group of patients and thesubject patients based on the risk of the disease. ARP program 112determines if the risk prediction model is accurate. If the riskprediction model is not accurate enough, then ARP program 112 returns toidentifying a neighboring group of patients to the subject patient basedon the risk of the disease. If the risk prediction model is accurateenough, ARP program 112 estimates the risk of the subject patient.

The risk prediction model created by ARP program 112 contains a numberof variables that will now be defined. There are a set of

patients

={p₁,p₂,p₃ . . . , p

}, and each patient is defined as a classification problem on a set of

possible diseases (labels). The

patients were examined periodically, and were labeled since it is knownwhat diseases they eventually suffer from. A binary matrix B (B ∈

^(n×m)) carry the given labels (diseases), where b_(ij)=1 if patientp_(i) suffers from disease j, and b_(ij)=0 otherwise. Here,

_(pi) denotes a group of patients (neighbor set) which consists of thepatients that are similar (nearest neighbors) to patient p_(i). Fordifferent patients the size of the neighbor set may differ. A graph ofthe patients is constructed, which is fully defined by a patientsimilarity matrix S (sparse), where an entry S_(ij)=1 if patient i and jare exactly the same, and S_(ij)=0 if patient i and j are not similar.The relative similarity provided by medical experts are enforced to thelearning of the patient similarity matrix S, such that better patientsimilarity is learned from human feedback, which in turn produces abetter estimate of patient risks. S_(ij)≠S_(ji) is possible and allowed.The row or column vectors are often referred to as matrices, forinstance, i-th row and j-th column vectors of the matrix S are denotedas S_(i•) and S_(j•), respectively. The risk prediction model created byARP program 112 iterates between the learning of the patient similaritymatrix S—updating a row of S in each iteration based on the relativesimilarities provide by medical experts, and the queryselection—identify the most informative group of neighboring patients byordering.

A user interface (not shown) is a program that provides an interfacebetween a user and ARP program 112. Any or all of the steps performed byARP program 112 can be facilitated by the user interface on computer 110or any other computer connected to computer 110 via network 102. A userinterface refers to the information (such as graphic, text, and sound) aprogram present to a user and the control sequences the user employs tocontrol the program. There are many types of user interfaces. In oneembodiment, the user interface may be a graphical user interface (GUI).A GUI is a type of user interface that allows users to interact withelectronic devices, such as a keyboard and mouse, through graphicalicons and visual indicators, such as secondary notations, as opposed totext-based interfaces, typed command labels, or text navigation. Incomputers, GUIs were introduced in reaction to the perceived steeplearning curve of command-line interfaces, which required commands to betyped on the keyboard. The actions in GUIs are often performed throughdirect manipulation of the graphics elements.

EHR database 114 resides on computer 110. In another embodiment, EHRdatabase 114 may reside on another device or computer within dataprocessing environment 100 or any other device not within dataprocessing environment 100, accessible via network 102. A database is anorganized collection of data. Data found in a database is typicallyorganized to model relevant aspects of reality in a way that supportsprocesses requiring the information found in the database. EHR database114 can be implemented with any type of storage device capable ofstoring data that may be accessed and utilized by computer 110, such asa database server, a hard disk drive, or a flash memory. In otherembodiments, EHR database can represent multiple storage devices withincomputer 110.

Alternatively, EHR database 114 can be any computer readable storagemedium as found in the art. For example, the computer readable storagemedium can be a tangible device that can retain and store instructionsfor use by an instruction execution device. The computer readablestorage medium may be, for example, but is not limited to, an electronicstorage device, a magnetic storage device, an optical storage device, anelectromagnetic storage device, a semiconductor storage device, or anysuitable combination of the foregoing. A non-exhaustive list of morespecific examples of the computer readable storage medium includes thefollowing: a portable computer diskette, a hard disk, a random accessmemory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), a static random access memory(SRAM), a portable compact disc read-only memory (CD-ROM), a digitalversatile disk (DVD), a memory stick, a floppy disk, a mechanicallyencoded device such as punch-cards or raised structures in a groovehaving instructions recorded thereon, and any suitable combination ofthe foregoing.

EHR database 114 may include medical information about individualpatients. An EHR is a record in digital format that is theoreticallycapable of being shared across different health care settings and mayinclude a wide range of data, including, but not limited to,demographics, medical history, medication and allergies, immunizationstatus, laboratory test results, radiology images, vital signs, andpersonal statistics like age and weight. The EHR database 114 isdesigned to represent data that accurately captures the state of thepatient at all times. It allows for an entire patient history to beviewed without the need to track down the patient's previous medicalrecord volume and assists in ensuring data is accurate, appropriate, andlegible.

FIG. 2 is a flowchart of workflow 200 depicting operational steps foractive patient risk prediction, in accordance with an embodiment of thepresent invention. In one embodiment, the steps of the workflow areperformed by ARP program 112. Alternatively, steps of the workflow canbe performed by any other program while working with ARP program 112. Ina preferred embodiment, a user, via a user interface discussedpreviously, can invoke workflow 200 upon determining that they wouldlike predict a patient's risk. In an alternative embodiment, workflow200 can be invoked automatically under the control of another program,for example, upon the user entering data about a subject patient in theEHR record database 114 and that update being sent to ARP program 112 tobegin a step in workflow 200.

ARP program 112 receives electronic health records (EHR) about multiplepatients and in addition EHR about the subject patient (step S205). Inan embodiment, ARP program 112 may receive the information about themultiple patients and the subject patient information from a medicalexpert and store the information in EHR database 114. In an alternativeembodiment, the information about the multiple patients may already bestored in EHR database 114 from previous active patient riskpredictions. In yet another alternative embodiment, the informationabout multiple patients may be stored by a hospital or healthcarenetwork and ARP program 112 can access this information via network 102.

ARP program 112 creates a risk prediction model (step S210). ARP program112, using the EHR data, learns a prediction model, which will be laterused to estimate the risk that a patient will suffer from a particulardisease. The reconstruction error may be represented as Equation (1). Inan embodiment, the reconstruction weight (patient similarity matrix) Sis solved as a constrained least square problem. In an alternativeembodiment, it can be solved as a linear system of equations. In yetanother embodiment, it can be solved as a quadratic program (QP).

$\begin{matrix}{{(S)} = {\sum\limits_{i = 1}^{n}\; \left. ||{p_{i} - {\sum\limits_{p_{j} \in _{p_{i}}}{S_{ij}p_{j}}}} \right.||^{2}}} & (1)\end{matrix}$

An advantage of using a QP formulation is that additional constraints(such as non-negativity) can be added in, and thereby makes theformulation more flexible.

^(i) denotes the local covariance matrix of patient p_(i) (the term“local” refers to the fact that the patient is used as the mean in thecalculation of covariance). The definition of can be expressed as

^(i)=(1p_(i)−

_(p) _(i) ) (1p_(i)−

_(p) _(i) )^(T), where 1 denotes a column vector consisting of ones. Itshould be noted that the superscript “T” denotes “transpose”, a basicmatrix operation. Using the local covariance matrix, the reconstructionerror problem can be reformulated to a series of small QP problems (onefor each patient), since each row of S is independent of every other.Formally, a row vector S_(i) (the weights used to reconstruct patientp_(i) using its neighbors) in the similarity matrix S can be solved as aQP problem represented as Equation (2). It should be noted that the term“s.t.” is short for “subject to”.

$\begin{matrix}{{\min\limits_{s_{i}}\mspace{14mu} {S_{i}\mspace{14mu} \mathcal{L}^{i}S_{i}^{T}}}{{{{s.t.\mspace{14mu} S_{i}}\mspace{14mu} 1} = 1};}{{S_{ij} \geq 0},{\forall{j \in \left\{ {1,2,\cdots,n} \right\}}}}} & (2)\end{matrix}$

The unconstrained version of patient similarity can be learned usingEquation (2). The relative similarities (neighborhood ordering) areencoded into the formulation, such that the feedback from humans can beincorporated to the similarity matrix of patients. The QP formulation ofthe reconstruction error represented in Equation (2) allows ARP program112 to encode the neighborhood orderings as a set of linear constraintsto the patient similarity matrix S.

A simplified example to show the enforcement of relative similarities ona group of just three patients (the minimum number of patients for arelative patient similarity) can be shown where given that a patientp_(i) has two neighboring (similar) patients p_(a) and p_(b), andpatient p_(a) is more similar to patient p_(i) than p_(b). It is thenclaimed that the weight of p_(a) used to reconstruct p_(i) should begreater than the weight of p_(b), i.e., S_(ia)≥S_(ib). This relativesimilarity can be encoded to the QP formulation using the linearconstraint as represented in Equation (3). In Equation (3) e^(a) is asingle-entry column vector with the a-th entry being one and all theother entries being zeros. With the transivity of inequality, a completeordering on a group of neighboring patients can be enforced using a setof concatenating constraints. In an alternative example, if it isrequired that patient p_(a), p_(b), and p_(c) are decreasingly similarto patient p_(i), i.e., in terms of patient similarity they haveS_(ia)≥S_(ib)≥S_(ic). then this ordering can be enforced using twoconcatenating constraints, i.e., S_(i•)(e^(a)-e^(b))≥0 andS_(i•)(e^(b)-e^(c))≥0.

$\begin{matrix}{{\min\limits_{s_{i}}\mspace{14mu} {S_{i}\mspace{14mu} \mathcal{L}^{i}S_{i}^{T}}}{{{{s.t.\mspace{14mu} S_{i}}\mspace{14mu} \left( {e^{a} - a^{b}} \right)} \geq 0};}{{{S_{i}\mspace{14mu} 1} = 1};}{{S_{ij} \geq 0},{\forall{j \in \left\{ {1,2,\cdots,n} \right\}}}}} & (3)\end{matrix}$

ARP program 112 identifies a neighboring group to the subject patient(step S215). With the QP formulation shown in Equation (3), the patientsimilarity matrix S can be learned under the guidance of the relativesimilarities provided by medical experts. Next, we must address theinformative patient neighborhoods, which will be prompted to humanexperts as queries. ARP program 112 aims to choose the patientneighborhood which if queried (sorted by human experts) will have themost significant impact in terms of better propagating the risk ofdiseases on the patient graph. Since each neighboring set of patientsnaturally forms a subset of the n patients, the counter set cover isused to estimate the importance of a patient neighborhood.

A cover set problem consists of two parts: (i) a universe which in ourcase is a patient set

containing all the n patients; and (ii) a set of subsets of

which in our case is the n patient neighbor sets that correspond to then patients, i.e.,

={

_(p1),

_(p2), . . . ,

_(pn)}. A subset

_(S) of

_(S)(

_(S) ⊂

) is a cover of the universe

if every patient in

appears at least once in

_(S). In other words, the union of the subsets in

_(S) is the universe, i.e., ∪

_(S) _(i) =

. A cover

_(S) that has minimum (possibly weighted) cardinality is called aminimum set cover. The set cover problem, which aims to identify such aminimum cover, is represented as Equation (4), where

_(i) is the indicator of the subset

_(p) _(i) (the neighborhood of patient p_(i)), which is set to 1 if theneighborhood

_(p) _(i) is part of the minimum set cover, and 0 otherwise.

_(ij) indicates whether the patient p_(i) exists in the neighborhood

_(p) _(j) (the neighborhood of patient p_(j)), i.e.,

_(ij)=1 if p_(i) ∈

_(p) _(j) and

_(ij)=0 otherwise. The first constraint in Equation (4) is to guaranteethat every patient in

is covered at least once in the solution, and the second constraint isto enforce the set cover indicator to be binary, i.e.,

_(i) is either 0 or 1.

min  ∑ i = 1 n   i   s . t . ∑ j = 1 n   ℬ ij  j ≥ 1 , ∀ p i ∈   i ∈ { 0 , 1 } ( 4 )

The set cover is a well studied NP-hard (Non-deterministicPolynomial-time hard) problem. The following greedy approximationalgorithm is used to solve the set cover problem: in each step, choosethe subset

_(p) _(i) that contains the most uncovered patients and repeat thisprocess until all patients are covered. This simple greedy approachfinds a set cover with at most c* log_(e) n sets, where an optimalsolution contains c*sets. With random initializations this methodproduces multiple close to minimum set covers. This allows the number ofsolutions that each patient neighborhood

_(p) _(i) participates in to be counted and make the estimation of eachneighborhood's significance easier.

(

_(p) _(i) ) denotes the significance of patient p_(i)'s neighborhood tomaintain the graph structure. The weighted counting set cover problem isrepresented as Equation (5), where z_(j) denotes a close to minimum setcover solution, and Z denotes the collection of the multiple close tominimum set covers. γ(

_(p) _(i) , z_(j)) indicates whether the neighborhood

_(p) _(i) is part of the (close to minimum) set cover z_(j). Formally,γ(

_(p) _(i) , z_(j))=1 if

_(p) _(i) ∈ z_(j), and γ(

_(p) _(i) , z_(j))=0 otherwise. w(

_(p) _(i) ) is the counting weight of patient neighborhood

_(p) _(i) , which also can be viewed as defining the querying preferenceof patient neighborhoods.

$\begin{matrix}{{\left( _{p_{i}} \right)} = {\sum\limits_{z_{j} \in }{{\gamma \left( {_{p_{i}},z_{j}} \right)}{w\left( _{p_{i}} \right)}}}} & (5)\end{matrix}$

In an embodiment, a uniform weighting scheme, represented as Equation(6) is used. This is a baseline weighting scheme that assigns a uniformweight to all patient neighborhoods. The underlying assumption of thisweighing scheme is that all patient neighborhoods are equally importantin the counting, and therefore, from the weighting perspective they areequally likely to be selected.

w(

_(p) _(i) )=1, ∀

_(p) _(i) ∈

  (6)

In an alternative embodiment, a connectivity weighting scheme,represented as Equation (7) is used. The counting weight of aneighborhood

_(p) _(i) is proportional to the frequency that the members of

_(p) _(i) is are used to reconstruct others. This weighting scheme isnode (patient) connectivity based, which assigns higher weights to thepatient neighborhoods that are located in the “dense” area of thepatient similarity matrix S. That is where the learning algorithm ismore likely to be confused. This implies that the weighting schemeprefers to query the patient neighborhoods that are highly connect toothers, including both within and outside the neighborhood, since theyare more influential in maintaining the key structure of the patientgraph.

$\begin{matrix}{{\left( _{p_{i}} \right)} = {\sum\limits_{j = 1}^{n}\; S_{ji}}} & (7)\end{matrix}$

ARP program 112 receives an experts ordering of the determinedneighboring group and the patient (step S220). Once an informativepatient neighborhood is identified by the counting set cover strategy(step S215), a medical expert will be asked to sort the neighbors indescending order with respect to the similarity to the original patientthat they are neighbors of. The relative similarities obtained fromhuman experts will be later incorporated to the learning of the patientsimilarity matrix S, as determined in step S210, which in turn improvisethe prediction accuracy of patient risks.

ARP program 112 updates the risk prediction model (step S225). Asdiscussed previously, Equation (2) is used to incorporate the feedbackof the ordering of neighboring groups and the original patient, fromstep S220, into the risk prediction model created in step S210. Thelearning of similarity is constrained by the relative ordering (feedbackfrom humans), which leads to the type of similarity that humans prefer.The QP formulation of the reconstruction error in Equation (2) allowsfor the encoding of the neighborhood orderings as a set of linearconstraints to the patient similarity matrix S. With the QP formulationshown in Equation (3), the risk prediction model can be updated with theinclusion of the similarities provided by medical experts.

ARP program 112 determines if the risk prediction model is accurate(decision block S230). In an embodiment, the risk prediction model willbe determined to be accurate when updating the risk prediction model(step S225), based on the medical experts ordering of neighboring groupsand the original patient (step S220), does not change the riskprediction model. In an alternative embodiment, the risk predictionmodel will be determined to be accurate when stopping criterion issatisfied. For example, after three iterations of determiningneighboring groups and medical experts ordering the neighboring groupsand the original patient. Alternatively, when the patient similarityconverges in the constrained (by the human feedback) similarity learningprocess, the risk prediction model can be determined to be accurate,since patient similarity is the (underlying) key of the risk predictionmodel.

If the risk prediction model is not accurate (decision block S230, falsebranch), then ARP program 112 proceeds to identify a new neighboringgroup (step S215). If the risk prediction model is accurate (decisionblock S230, true branch), then ARP program 112 proceeds to estimatepatient risk (step S235).

ARP program estimates patient risk (step S235). After the activelearning of patient similarity matrix S, patient risk prediction can beperformed using graph diffusion methods. In particular, the givens risksof diseases are propagated on the patient graph using the similaritymatrix S. Each row of the patient similarity matrix S sums to one,thereby S can be readily used as the transition matrix and perform arandom walk on the graph to infer patients risks. In each riskpropagation iteration, the state (i.e. the risks of the diseases), ofeach patient is partially (with a rate of λ) adjusted by risk valuesthat flow on the graph, but still preserve a portion (with a rate of1−λ) of the given true risks.

denotes the predicted patient risk and

denotes the given true risk, the state (risk) of patients at time t+1can be inferred from the previous state of patients at time t,represented by Equation (8).

^(t+1) =λS

^(t)+(1−λ)

  (8)

^(∞) denotes the patient state (risk) after infinite random walk steps,as represented by Equation (9), and the state of patients eventuallyconverges to a steady-state probability, where I denotes the identitymatrix. The value of (1−λ) can be interpreted as the probability of therestart (jump back to the initial state) in a random walk. The restartis a necessary step in the risk propagation process, otherwise theproblem would reduce to a global solution, which is equivalent to theresult of PageRank. PageRank is a ranking method that ranks nodes (basedon their “popularity”) on a graph, for example, search engines may usePageRank type method to rank webpages. (1−λ) can also be viewed as theconstant to penalize the changes to the initial risk. I the given risk

is relatively more complete (

is a dense matrix), a smaller value should be set for λ. Alternatively,the value of λ should be larger if the given risk

is relatively less complete (

is a sparse matrix) or contains a considerable amount of noise.

^(∞)=(1−λ)(I−λS)⁻¹

  (9)

In an example, the final goal is to predict if a person is mentallyhealthy based on his or her structural MRI scan. Typically, this is adifficult problem to solve since there is not enough training data toobtain an accurate prediction model. Such types of training data is hardand expensive to obtain since it is difficult to track the health recordof patients (patients may move to another place, may go to anotherhospital, or may not want to share his or her medical records).Additionally, it requires a doctor to determine if a patient is mentallyhealthy or not, and the labor expense of doctors can be quite high.Typical questions can be very challenging to answer. For example, willthis patient suffer from Alzheimer's later in his or her life? This is adifficult question even for a doctor. Alternatively, are Patient 1 andPatient 2 similar or not? This question cannot be answered without amedical background.

Using the above described method, it is not necessary to determine if apatient is healthy or not, rather the relative similarity betweenpatients is compared, which is much easier and can be done even withouta medical background. For example, is Patient 2 or Patient 3 moresimilar to Patient 1? This is an easy question, since people withoutmedical background can answer this question by simply comparing threeimages in the case of a structural MRI scan. In this way, the abovedescribed method significantly reduces the cost of the collection ofmedical training data, which in turn makes the risk prediction modelpossible or more accurate.

FIG. 3 depicts a block diagram of components of computer 300, inaccordance with an illustrative embodiment of the present invention. Inan embodiment, computer 300 is representative of computer 110. It shouldbe appreciated that FIG. 3 provides only an illustration of oneimplementation and does not imply any limitations with regard to theenvironments in which different embodiments may be implemented. Manymodifications to the depicted environment may be made.

Computer 300 includes communications fabric 302, which providescommunications between computer processor(s) 304, memory 306, persistentstorage 308, communications unit 310, and input/output (I/O)interface(s) 312. Communications fabric 302 can be implemented with anyarchitecture designed for passing data and/or control informationbetween processors (such as microprocessors, communications and networkprocessors, etc.), system memory, peripheral devices, and any otherhardware components within a system. For example, communications fabric302 can be implemented with one or more buses.

Memory 306 and persistent storage 308 are computer readable storagemedia. In this embodiment, memory 306 includes random access memory(RAM) 314 and cache memory 316. In general, memory 306 can include anysuitable volatile or non-volatile computer readable storage media.Software and data 322 are stored in persistent storage 308 for accessand/or execution by processors 304 via one or more memories of memory306. With respect to computer 110, software and data 322 includes ARPprogram 112 and EHR database 114.

In this embodiment, persistent storage 308 includes a magnetic hard diskdrive. Alternatively, or in addition to a magnetic hard disk drive,persistent storage 308 can include a solid state hard drive, asemiconductor storage device, read-only memory (ROM), erasableprogrammable read-only memory (EPROM), flash memory, or any othercomputer readable storage media that is capable of storing programinstructions or digital information.

The media used by persistent storage 308 may also be removable. Forexample, a removable hard drive may be used for persistent storage 308.Other examples include optical and magnetic disks, thumb drives, andsmart cards that are inserted into a drive for transfer onto anothercomputer readable storage medium that is also part of persistent storage308.

Communications unit 310, in these examples, provides for communicationswith other data processing systems or devices. In these examples,communications unit 310 may include one or more network interface cards.Communications unit 310 may provide communications through the use ofeither or both physical and wireless communications links. Software anddata 322 may be downloaded to persistent storage 308 throughcommunications unit 310.

I/O interface(s) 312 allows for input and output of data with otherdevices that may be connected to computer 300. For example, I/Ointerface 312 may provide a connection to external devices 318 such as akeyboard, keypad, a touch screen, and/or some other suitable inputdevice. External devices 318 can also include portable computer readablestorage media such as, for example, thumb drives, portable optical ormagnetic disks, and memory cards. Software and data used to practiceembodiments of the present invention, e.g., ARP program 112, can bestored on such portable computer readable storage media and can beloaded onto persistent storage 308 via I/O interface(s) 312. I/Ointerface(s) 312 also can connect to a display 320.

Display 320 provides a mechanism to display data to a user and may be,for example, a computer monitor. Display 320 can also function as atouch screen, such as a display of a tablet computer.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. A method for updating a patient risk predictionmodel, the method comprising: identifying, by one or more computerprocessors, a neighboring group of patients with respect to an originalpatient based on electronic health records of each of the respectivepatients, wherein the neighboring group of patients is two or morepatients similar to the original patient; generating, by one or morecomputer processors, a question as to a relative ordering of the two ormore patients of the neighboring group of patients with respect to theoriginal patient; receiving an answer to the question as to the relativeordering of the two or more patients of the neighboring group ofpatients, wherein the ordering of the two or more patients of theneighboring group of patients is based upon how similar each patient ofthe two or more patients is to the original patient; and updating, byone or more computer processors, a risk prediction model based on theanswer to the question as to the relative ordering of the two or morepatients of the neighboring group of patients.
 2. The method of claim 1,further comprising: estimating, by one or more computer processors, therisk that the original patient will suffer from the disease based uponthe updated risk prediction model.
 3. The method of claim 1, wherein theordering of the patients of the neighboring group of patients is acomplete ordering including all patients of the neighboring group ofpatients or a partial ordering including at least one of the patients ofthe neighboring group of patients.
 4. The method of claim 1, wherein therisk prediction model for a disease based on the plurality of patientsis selected from a group consisting of: constrained least squareproblem, a linear system of equations, or a quadratic program.
 5. Themethod of claim 1, wherein the risk prediction model is updated until apatient similarity converges in a constrained similarity process.
 6. Themethod of claim 1, wherein the risk prediction model is updated morethan one time.
 7. The method of claim 1, wherein the electronic healthrecord includes one or more of the following: demographics; medicalhistory; medication and allergies; immunization status; laboratory testresults; radiology images; vital signs; and personal statistics.
 8. Acomputer program product for updating a patient risk prediction model,the computer program product comprising: one or more computer readablestorage media and program instructions stored on the one or morecomputer readable storage media, the program instructions comprising:program instructions to identify a neighboring group of patients withrespect to an original patient based on electronic health records ofeach of the respective patients, wherein the neighboring group ofpatients is two or more patients similar to the original patient;program instructions to generate a question as to a relative ordering ofthe two or more patients of the neighboring group of patients withrespect to the original patient; program instructions to receive ananswer to the question as to the relative ordering of the two or morepatients of the neighboring group of patients, wherein the ordering ofthe two or more patients of the neighboring group of patients is basedupon how similar each patient of the two or more patients is to theoriginal patient; and program instructions to update a risk predictionmodel based on the answer to the question as to the relative ordering ofthe two or more patients of the neighboring group of patients.
 9. Thecomputer program product of claim 8, further comprising programinstructions, stored on the one or more computer readable storage media,to: estimate the risk that the original patient will suffer from thedisease based upon the updated risk prediction model.
 10. The computerprogram product of claim 8, wherein the ordering of the patients of theneighboring group of patients is a complete ordering including allpatients of the neighboring group of patients or a partial orderingincluding at least one of the patients of the neighboring group ofpatients.
 11. The computer program product of claim 8, wherein the riskprediction model for a disease based on the plurality of patients isselected from a group consisting of: constrained least square problem, alinear system of equations, or a quadratic program.
 12. The computerprogram product of claim 8, wherein the risk prediction is updated untila patient similarity converges in a constrained similarity process. 13.The computer program product of claim 8, wherein the risk predictionmodel is updated more than one time.
 14. The computer program product ofclaim 8, wherein the electronic health record includes one or more ofthe following: demographics; medical history; medication and allergies;immunization status; laboratory test results; radiology images; vitalsigns; and personal statistics.
 15. A computer system for updating apatient risk prediction model, the computer system comprising: one ormore computer processors; one or more computer readable storage media;and program instructions stored on the computer readable storage mediafor execution by at least one of the one or more processors, the programinstructions comprising: program instructions to identify a neighboringgroup of patients with respect to an original patient based onelectronic health records of each of the respective patients, whereinthe neighboring group of patients is two or more patients similar to theoriginal patient; program instructions to generate a question as to arelative ordering of the two or more patients of the neighboring groupof patients with respect to the original patient; program instructionsto receive an answer to the question as to the relative ordering of thetwo or more patients of the neighboring group of patients, wherein theordering of the two or more patients of the neighboring group ofpatients is based upon how similar each patient of the two or morepatients is to the original patient; and program instructions to updatea risk prediction model based on the answer to the question as to therelative ordering of the two or more patients of the neighboring groupof patients.
 16. A computer system of claim 15, further comprisingprogram instructions, stored on the one or more computer readablestorage media for execution by the at least one of the one or morecomputer processors, to: estimate the risk that the original patientwill suffer from the disease based upon the updated risk predictionmodel.
 17. A computer system of claim 15, wherein the ordering of thepatients of the neighboring group of patients is a complete orderingincluding all patients of the neighboring group of patients or a partialordering including at least one of the patients of the neighboring groupof patients.
 18. A computer system of claim 15, wherein the riskprediction model for a disease based on the plurality of patients isselected from a group consisting of: constrained least square problem, alinear system of equations, or a quadratic program.
 19. A computersystem of claim 15, wherein the risk prediction model is updated morethan one time.
 20. A computer system of claim 15, wherein the electronichealth record includes one or more of the following: demographics;medical history; medication and allergies; immunization status;laboratory test results; radiology images; vital signs; and personalstatistics.